634 research outputs found
Dynamics of Primordial Hydrogen Recombination with Allowance for a Recoil for Scattering in the Ly-alpha Line
It is shown that taking into account a recoil for radiation scattering in the
Ly-alpha line can lead to a noticable acceleration of primordial hydrogen
recombination. Thus for LambdaCDM model a decrease of ionization degree exceeds
1% for redshifts z in a range 800 - 1050 achieving approximately 1.3% at z=900.
Corresponding corrections to the cosmic microwave background power spectra can
achieve 1.1% for TT spectra and 1.7% for EE ones. Radiative transfer in these
calculations was treated in a quasistationary approximation. Numerical
solutions are also obtained in diffusion approximation for a nonstationary
problem of Ly-alpha line radiative transfer under partial frequency
redistribution with a recoil. An evolution of a local line profile is traced to
as well as an evolution of a relative number of uncompensated transitions from
2p state down to 1s one. It is shown that taking into account nonstationarity
of Ly-alpha line radiative transfer can lead to an additional acceleration of
primordial hydrogen recombination.Comment: 9 pages, 5 figures; accepted for publication in Astronomy Letter
Motivation to football students of higher educational institutions
The aim of this work is to define factors contributing to increased motivation to playing football in the system of sports and recreational activities. Football is regarded as a kind of recreational activity. It is established that for most students, classes recreational games are a means of promoting health, well-being, improve the bodyЦелью работы является определение факторов, способствующих повышению мотивации к занятиям футболом в системе физкультурно-оздоровительных занятий. Рассматривается футбол как вид рекреационной деятельности. Установлено, что для большинства студентов занятия рекреационными играми являются средством укрепления здоровья, хорошего самочувствия, улучшения телосложени
Thermal fractionation of air in polar firn by seasonal temperature gradients
Air withdrawn from the top 5-15 m of the polar snowpack (firn) shows anomalous enrichment of heavy gases during summer, including inert gases. Following earlier work, we ascribe this to thermal diffusion, the tendency of a gas mixture to separate in a temperature gradient, with heavier molecules migrating toward colder regions. Summer warmth creates a temperature gradient in the top few meters of the firn due to the thermal inertia of the underlying firn and causes gas fractionation by thermal diffusion. Here we explore and quantify this process further in order to (1) correct for bias caused by thermal diffusion in firn air and ice core air isotope records, (2) help calibrate a new technique for measuring temperature change in ice core gas records based on thermal diffusion [Severinghaus et al., 1998], and (3) address whether air in polar snow convects during winter and, if so, whether it creates a rectification of seasonality that could bias the ice core record. We sampled air at 2-m-depth intervals from the top 15 m of the firn at two Antarctic sites, Siple Dome and South Pole, including a winter sampling at the pole. We analyzed 15N/14N, 40Ar/36Ar, 40Ar/38Ar, 18O/16O of O2, O2/N2, 84Kr/36Ar, and 132Xe/36Ar. The results show the expected pattern of fractionation and match a gas diffusion model based on first principles to within 30%. Although absolute values of thermal diffusion sensitivities cannot be determined from the data with precision, relative values of different gas pairs may. At Siple Dome, δ40Ar/4 is 66 ± 2% as sensitive to thermal diffusion as δ15N, in agreement with laboratory calibration; δ18O/2 is 83 ± 3%, and δ84Kr/48 is 33 ± 3% as sensitive as δ15N. The corresponding figures for summer South Pole are 64 ± 2%, 81 ± 3%, and 34 ± 3%. Accounting for atmospheric change, the figure for δO2/N2/4 is 90 ± 3% at Siple Dome. Winter South Pole shows a strong depletion of heavy gases as expected. However, the data do not fit the model well in the deeper part of the profile and yield a systematic drift with depth in relative thermal diffusion sensitivities (except for Kr, constant at 34 ± 4%), suggesting the action of some other process that is not currently understood. No evidence for wintertime convection or a rectifier effect is seen
The basic methodology of physical therapy for diseases of the respiratory system
The article discusses the methods of exercise therapy for diseases of the respiratory system, types of exercises, indications for their use and the processes that occurВ статье рассматриваются методики ЛФК при заболевании дыхательной системы, виды упражнений, показания к их применению и процессы, которые при этом происходя
Two-Photon 2s<->1s Transitions during Recombination of Hydrogen in the Universe
Based on the standard cosmological model, we calculate the correction to the
rate of two-photon 2s1s transitions in the hydrogen atom under primordial
hydrogen plasma recombination conditions that arises when the induced
transitions under equilibrium background radiation with a blackbody spectrum
and plasma recombination radiation are taken into account.Comment: 20 pages, 9 figure
Ignition of premixed air/fuel mixtures by microwave steamer discharge
A variety of methods exists for fast and efficient combustion of air-fuel mixtures. In this study, a microwave subcritical streamer discharge is used to ignite propane-air mixtures at atmospheric pressure. The streamer is initiated at the inner surface of a dielectric tube with the help of a passive half-wave vibrator. By creating a network of ignition lines, the streamer discharge forms the network of burning channels with large total surface area. This leads to the apparent speed of combustion propagation along the cylinder in excess of 100 m/s, which is more than 200 times the laminar flame propagation speed. The axial propagation of the combustion front in a cylindrical tube filled with the air/propane mixture is investigated by high speed video recording in visible light. A simple model is presented to explain observed results
Study on influence of two-phase filtration transformation on formation of zones of undeveloped oil reserves
In order to study the process of fluid filtration during flooding of an oil field, article uses Rapoport – Lis model of non-piston oil displacement by water. During plane-radial filtration in a homogeneous formation, radii of disturbance zones are determined with and without taking into account the end effect. Influence of changes in value of capillary pressure gradient on distribution of water saturation coefficient in the non-piston displacement zone for high and low permeability reservoirs is revealed. Application of an element model for a five-point injection and production well placement system showed that, using traditional flooding technology, flat-radial fluid filtration is transformed into rectilinear-parallel. At solving equation of water saturation, Barenblatt method of integral relations was used, which allows determining the transformation time. By solving the saturation equation for rectilinear-parallel filtration, change in the value of water saturation coefficient at bottomhole of production well for an unlimited and closed deposit is determined. It is shown that an increase in water cut coefficient of a production well is possible only for a closed formation. To determine coefficient of water saturation in a closed deposit, a differential equation with variable coefficients is obtained, an iterative solution method is proposed. In the element of the five-point system, oil-saturated zones not covered by development were identified. For channels of low filtration resistance, conditions for their location in horizontal and vertical planes are established. It is shown that, at maintaining formation pressure, there is an isobar line in formation, corresponding to initial formation pressure, location of which determines direction of fluid crossflow rates. Intensity of crossflows affects application efficiency of hydrodynamic, physical and chemical, thermal and other methods of enhanced oil recovery
Elastic Spin Relaxation Processes in Semiconductor Quantum Dots
Electron spin decoherence caused by elastic spin-phonon processes is
investigated comprehensively in a zero-dimensional environment. Specifically, a
theoretical treatment is developed for the processes associated with the
fluctuations in the phonon potential as well as in the electron procession
frequency through the spin-orbit and hyperfine interactions in the
semiconductor quantum dots. The analysis identifies the conditions (magnetic
field, temperature, etc.) in which the elastic spin-phonon processes can
dominate over the inelastic counterparts with the electron spin-flip
transitions. Particularly, the calculation results illustrate the potential
significance of an elastic decoherence mechanism originating from the
intervalley transitions in semiconductor quantum dots with multiple equivalent
energy minima (e.g., the X valleys in SiGe). The role of lattice anharmonicity
and phonon decay in spin relaxation is also examined along with that of the
local effective field fluctuations caused by the stochastic electronic
transitions between the orbital states. Numerical estimations are provided for
typical GaAs and Si-based quantum dots.Comment: 57 pages, 14 figure
Do Substance P and Neurokinin A Play Important Roles in the Control of LH Secretion in Ewes?
There is now general agreement that neurokinin B (NKB) acts via neurokinin-3-receptor (NK3R) to stimulate secretion of GnRH and LH in several species, including rats, mice, sheep, and humans. However, the roles of two other tachykinins, substance P (SP) and neurokinin A, which act primarily via NK1R and NK2R, respectively, are less clear. In rodents, these signaling pathways can stimulate LH release and substitute for NKB signaling; in humans, SP is colocalized with kisspeptin and NKB in the mediobasal hypothalamus. In this study, we examined the possible role of these tachykinins in control of the reproductive axis in sheep. Immunohistochemistry was used to describe the expression of SP and NK1R in the ovine diencephalon and determine whether these proteins are colocalized in kisspeptin or GnRH neurons. SP-containing cell bodies were largely confined to the arcuate nucleus, but NK1R-immunoreactivity was more widespread. However, there was very low coexpression of SP or NK1R in kisspeptin cells and none in GnRH neurons. We next determined the minimal effective dose of these three tachykinins that would stimulate LH secretion when administered into the third ventricle of ovary-intact anestrous sheep. A much lower dose of NKB (0.2 nmol) than of neurokinin A (2 nmol) or SP (10 nmol) consistently stimulated LH secretion. Moreover, the relative potency of these three neuropeptides parallels the relative selectivity of NK3R. Based on these anatomical and pharmacological data, we conclude that NKB-NK3R signaling is the primary pathway for the control of GnRH secretion by tachykinins in ewes
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